Field of the Invention
A field bus coupler, and method, operable in a normal mode for connecting an input/output module to the field bus of a control computer, and in a diagnostic mode for sending diagnostic values to the control computer and to the input/output module.
Description of Related Art
In industrial automation systems, field buses for transmitting control data and/or measured values between one or more central control computers, also called master computers or programmable logic controllers (PLC), and field devices are interchanged. Field devices include input and output modules, for example, hereinafter abbreviated to I/O (input/output) modules, which provide analog and/or digital input and/or output channels via which system components can be controlled and via which measured values, for example from sensors, can be read in. Frequently, rather than being connected to the fieldbus directly, each individual field device is connected thereto via a field bus coupler, which acts as a data interface between the fieldbus on one side and an often proprietary sub-bus on the other. A multiplicity of bus-capable modules, for example the stated I/O modules, can be coupled to the sub-bus.
A field bus coupler of this type, also called a field bus gateway, is generally also used for configuring the connected modules. For this purpose, a web server is frequently provided in the field bus coupler, via which the field bus coupler itself along with the connected modules are configured using a web browser which is run in an external (service) computer. The field bus coupler usually comprises for this purpose a service interface, for example a USB (universal serial bus) data interface, via which the field bus coupler can be configured on site, for example by a service technician.
When the industrial automation system is operating, the field bus coupler receives output values for the individual I/O modules via the field bus, and forwards these via the sub-bus to the corresponding I/O module, which adjusts its output channels accordingly. Conversely, signals that have been analyzed by the I/O module, for example sensor signals, are converted to input values and are transmitted via the sub-bus to the field bus coupler. The field bus coupler forwards the input values via the field bus to the higher level control system.
During start up or during a diagnostic search in a system of this type, it is frequently helpful or essential to define specific output values for an output channel of an I/O module independently of the actual program sequence of the control program and/or to be capable of testing a reaction of the control program to certain input signals, even if these input signals are not present at the time. For this purpose, the control program is usually modified periodically, to allow specific output values to be defined independently of the actual program sequence. Similarly, it is standard practice during a diagnostic search to periodically set variables of the control program which reflect input values that have been read in to a desired value manually by inputting a corresponding program command, in order to enable the continued program sequence for said input value to be simulated. In many development environments for control programs, a so-called debugging mode is also provided, which can be used to set variables to desired values. An alternative procedure for specifying input signals involves connecting an adjustable current or voltage source, with which specific sensor signals can be simulated, to an input channel of an I/O module rather than to an input channel of a sensor.
However, manipulating a control program, whether manually or via a development system, is costly and also involves the risk that the control program may be altered beyond the desired manipulations. Moreover, when a system is being placed in operation, a control program that can be manipulated is not yet available or is not yet fully available. Using an adjustable current source or voltage source in place of a sensor requires rewiring.
The present invention was developed to provide a method by which a diagnostic search can be carried out in a remote I/O system without requiring that a control program that is ordinarily used must be manipulated for this purpose, and without requiring periodic rewiring.